Autotools update

Adds --disable-vec option to add the following flags:

• GCC: -fno-tree-vectorize
• ICC: -no-vec -no-simd
• CLANG: -fno-vectorize -fno-slp-vectorize"

There is no --enable-vec, that is a noop.

configure.ac

@@ -216,6 +216,32 @@ if test "$enable_san" = "yes"; then
fi
fi
+#  Disable vectorisation for known compilers. This switches off optimizations
+#  that could be enabled above, so in general should be appended. Slightly odd
+#  implementation as want to describe as --disable-vec, but macro is enable
+#  (there is no enable action).
+AC_ARG_ENABLE([vec],
+   [AS_HELP_STRING([--disable-vec],
+     [Disable vectorization]
+   )],
+   [enable_vec="$enableval"],
+   [enable_vec="yes"]
+)
+if test "$enable_vec" = "no"; then
+   if test "$ax_cv_c_compiler_vendor" = "intel"; then
+      CFLAGS="$CFLAGS -no-vec -no-simd"
+      AC_MSG_RESULT([disabled Intel vectorization])
+   elif test "$ax_cv_c_compiler_vendor" = "gnu"; then
+      CFLAGS="$CFLAGS -fno-tree-vectorize"
+      AC_MSG_RESULT([disabled GCC vectorization])
+   elif test "$ax_cv_c_compiler_vendor" = "clang"; then
+      CFLAGS="$CFLAGS -fno-vectorize -fno-slp-vectorize"
+      AC_MSG_RESULT([disabled clang vectorization])
+   else
+      AC_MSG_WARN([Do not know how to disable vectorization for this compiler])
+   fi
+fi
+
# Autoconf stuff.
AC_PROG_INSTALL
AC_PROG_MAKE_SET